Certain spinal conditions, including a fracture of a vertebra and a herniated disc, indicate treatment by spinal immobilization. Several methods of spinal immobilization are known, including surgical fusion and the attachment of pins and bone plates to the affected vertebras.
Spinal immobilization systems typically require the threaded securement of some form of bone anchor and the like or bone screw-assembly into two or more vertebrae, which entails drawing the rod to the anchors/screw-assemblies or drawing the anchors/screw-assemblies to the rod. Spinal screw-assemblies are used to secure a stabilization rod and comprise various components including a pedicle screw and a body member. The design of the spinal screw-assemblies allows for variable angular movement of the body member with respect to the pedicle screw with a threaded shaft portion of the screw extending through an opening in an end of the body member. However, in these systems, in order to tighten the spinal screw-assembly at a specific angle, a rod, and set screw must first be inserted, the components are tightened, and then the rod and set screw are removed.